Batteries including a flat plate design

ABSTRACT

A battery having flat, stacked, anode and cathode layers. The battery can be adapted to fit within an implantable medical device.

RELATED APPLICATION

This application claims the benefit under 35 U.S.C. 119(e) of U.S.Provisional Application Ser. No. 60/437,537 filed Dec. 31, 2002, thespecification of which is hereby incorporated by reference.

TECHNICAL FIELD

The present invention concerns implantable medical devices, such asdefibrillators and cardioverters, and more specifically to a battery forsuch devices.

BACKGROUND

Patients prone to irregular heart rhythms sometimes have miniature heartdevices, such as defibrillators and cardioverters, implanted in theirbodies. These devices detect onset of abnormal heart rhythms and applycorrective electrical therapy to the heart. The defibrillator orcardioverter includes a set of electrical leads, which extend from adevice housing into the heart. Within the device housing are a batteryfor supplying power, circuitry for detecting abnormal heart rhythms, anda capacitor for delivering bursts of electric current through the leadsto the heart. Since defibrillators and cardioverters are typicallyimplanted in the left region of the chest or in the abdomen, a smallersize device, which is still capable of delivering the required level ofelectrical energy, is desirable.

The basic components that make up a battery are an anode, a cathode, aseparator between the anode and the cathode, electrolyte, and packaginghardware such as the case. Batteries can be of a wound, jellyroll, styleof design that may be cylindrical or flattened cylindrical in shape.Some designs fold the battery components on top of one another.

The anodes and cathodes of the battery are opposed to each otherthroughout the battery. This continuous opposition requirement createspackaging inefficiencies, such as wasted volume at bend lines or, in thewound configuration, the mandrel volume itself. Moreover, these foldedor wound design approaches are limited to simple cross-sectional areasdue to the manufacturing constraints of producing such a battery cell.It is desirable to improve the packaging efficiency of the batteryparticularly for medical implantable devices, since this will provide asmaller battery. Also, consistency from one battery to the next is adesirable feature for implantable medical devices. A heightenedconsistency allows the battery's life-cycle to be predictable and allowsthe battery to be replaced at an opportune time without emergency.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is an exploded perspective view of a flat battery according toone embodiment.

FIG. 2 is an exploded perspective view of the battery stack of FIG. 1.

FIG. 3 is a perspective view of an anode according to one embodiment.

FIG. 4A is a front view of an anode collector manifold according to oneembodiment.

FIG. 4B shows a detailed portion of the anode collector manifold of FIG.4A.

FIG. 5 shows a front view of an anode collector according to oneembodiment.

FIG. 6 shows a front view of an anode collector according to oneembodiment.

FIG. 7 shows a front view of an anode collector according to oneembodiment.

FIG. 8 shows a front view of an anode collector according to oneembodiment.

FIG. 9 shows an exploded view of a cathode assembly according to oneembodiment.

FIG. 10 is a front view of a cathode collector manifold according to oneembodiment.

FIG. 11A shows a front view of a cathode collector according to oneembodiment.

FIG. 11B shows a detailed portion of the cathode collector of FIG. 11A.

FIG. 12 shows a front view of a cathode collector according to oneembodiment.

FIG. 13 shows a front view of a cathode collector according to oneembodiment.

FIG. 14 shows a front view of a cathode collector according to oneembodiment.

FIG. 15 shows a perspective view of an alignment fixture forconstructing a battery stack according to one embodiment.

FIG. 16 is a perspective view of a battery stack within the fixture ofFIG. 15.

FIG. 17 is a top view of FIG. 16.

FIG. 18A shows a sectional front view of a stacking fixture forconstructing a battery stack according to one embodiment.

FIG. 18B shows a perspective view of a stacking fixture for constructinga battery stack according to one embodiment.

FIG. 18C shows a detail of the upper members of the stacking fixture ofFIG. 18B.

FIG. 18D shows an upper member of the stacking fixture of FIG. 18B,according to one embodiment.

FIG. 18E shows an upper member of the stacking fixture of FIG. 18B,according to one embodiment.

FIG. 18F shows a schematic front view of the stacking fixture of FIG.18B.

FIG. 18G shows a front view of portion of a battery stack and an uppermember of a stacking fixture according to one embodiment.

FIG. 19 is a top view of a battery stack according to one embodiment.

FIG. 20 is a side schematic view of the battery stack of FIG. 19.

FIG. 21 is a perspective view of the battery stack of FIG. 1.

FIG. 22A is a side view of the battery stack of FIG. 1.

FIG. 22B is a perspective view of an insulating member according to oneembodiment.

FIG. 22C is a side view of the insulating member of FIG. 22B.

FIG. 23A shows a side view of the battery stack and battery case lid ofFIG. 1.

FIG. 23B shows a cross-section of the battery stack of FIG. 23A.

FIG. 23C shows a cross-section of the feedthrough assembly of thebattery of FIG. 23A.

FIG. 24A shows a side view of a battery according to one embodiment.

FIG. 24B shows a cross-section of the battery of FIG. 24A.

FIG. 24C shows a close-up detail of the cross-section of FIG. 24B.

FIG. 25 shows a perspective view of a battery according to oneembodiment.

FIG. 26A shows an exploded view of the battery of FIG. 25.

FIG. 26B shows a battery stack according to one embodiment.

FIG. 27 shows an exploded view of a battery stack according to oneembodiment.

FIG. 28 shows a top view of a cathode within a sealed separator,according to one embodiment.

FIG. 29 is a side view of a cathode sealed within a separator accordingto one embodiment.

FIG. 30 shows a side view of a detail of the upper portion of thecathode of FIG. 29.

FIG. 31 shows a side view of a detail of the lower portion of thecathode of FIG. 29.

FIG. 32 shows a top view of a cathode for a battery stack according toone embodiment.

FIG. 33 shows a top view of an anode for a battery stack according toone embodiment.

FIG. 34 shows a top view of a separator for a battery stack according toone embodiment.

FIG. 35 shows a top view of a battery stack having the cathode, anode,and separator of FIGS. 32-34.

FIG. 36A shows a top view of the extension members of the battery stackof FIG. 35.

FIG. 36B shows a top view of a cathode according to one embodiment.

FIG. 36C shows a side view of the cathode of FIG. 36B.

FIG. 36D shows a detail view of FIG. 36C.

FIG. 36E shows a partial perspective view of a battery according to oneembodiment.

FIG. 37 shows a top view of a cathode layer according to one embodiment.

FIG. 38 shows a top view of an anode layer according to one embodiment.

FIG. 39 shows a perspective view of a battery stack constructedaccording to one embodiment.

FIG. 40 shows a perspective view of the battery stack of FIG. 39.

FIG. 41 shows a perspective view of a taping fixture according to oneembodiment.

FIG. 42 shows a top view of the taping fixture of FIG. 41.

FIGS. 43A and 43B show top views of an example battery stack being tapedaccording to one embodiment.

FIGS. 44A and 44B show top views of an example battery stack being tapedaccording to one embodiment.

FIG. 45 shows a partial cut-away view of the terminal connections of abattery according to one embodiment.

FIG. 46 shows a partial top view of a battery according to oneembodiment.

FIG. 47A shows a section view of FIG. 46.

FIG. 47B shows another section view of FIG. 46.

FIG. 48A shows a terminal according to one embodiment.

FIG. 48B shows a side view of the terminal of FIG. 48A being attached toa case in accordance with one embodiment.

FIG. 48C shows a view of the terminal of FIG. 48A after being attachedto the case.

FIG. 48D shows a detail side view of a terminal according to oneembodiment.

FIGS. 49A, 49B, and 49C shows a backfill plug welding techniqueaccording to one embodiment.

FIG. 50A shows a backfill plug for a battery according to oneembodiment.

FIGS. 50B and 50C shows a backfill plug welding technique according toone embodiment.

FIG. 50D shows a backfill plug terminal for a battery according to oneembodiment.

FIG. 50E shows a backfill plug terminal for a battery according to oneembodiment.

FIG. 51 is a flowchart of a method of constructing a battery, inaccordance with one embodiment.

FIG. 52 shows a schematic view of a system for manufacturing anodes, inaccordance with one embodiment.

FIG. 53 shows a system for constructing cathodes, in accordance with oneembodiment.

FIG. 54 shows a schematic view of a fixture for constructing cathodes,in accordance with one embodiment.

FIG. 55 shows a side view of the fixture of FIG. 54.

FIG. 56 shows a schematic view of a system for constructing cathodes, inaccordance with one embodiment.

FIG. 57 shows a side view of the system of FIG. 56.

FIG. 58 shows a top view of a cathode forming fixture according to oneembodiment.

FIG. 59 shows a side view of the fixture of FIG. 58.

FIG. 60 shows a front view of the fixture of FIG. 58.

FIG. 61 is a block diagram of a implantable medical device systemaccording to one embodiment.

FIG. 62 is a chart of a battery constructed according tone embodiment.

DESCRIPTION OF EMBODIMENTS

In the following detailed description, reference is made to theaccompanying drawings which form a part hereof, and in which is shown byway of illustration specific embodiments in which the invention may bepracticed. These embodiments are described in sufficient detail toenable those skilled in the art to practice the invention, and it is tobe understood that other embodiments may be utilized and that structuralchanges may be made without departing from the scope of the presentinvention. Therefore, the following detailed description is not to betaken in a limiting sense, and the scope of the present invention isdefined by the appended claims and their equivalents.

FIG. 1 shows an exploded view of a battery 18 according to oneembodiment. The present embodiment shows a D-shaped battery. In otherembodiments, battery 18 can be designed in a variety of flat shapes toconform to various housing shapes. The discussion herein providestechniques to manufacture a battery having virtually any arbitraryshape, such as rectangular or non-rectangular. Moreover, the edges ofthe battery can be curved to allow the battery to fit in ashape-friendly curved case, as will be detailed below. The batteryincludes a metallic case 20 defining a chamber 22 which holds a batterystack 24. In one embodiment, case 20 is manufactured from a conductivematerial, such as stainless steel. In another option, the case 20 ismanufactured using a nonconductive material, such as a ceramic or aplastic.

Case 20 includes a base 26 and a lid 28 positionable on an upper rim 27of base 26. Battery stack 24 has a cutout region 34 at its periphery,with cutout region 34 being positioned when the stack 24 is installed incase 20 to provide space for electrical connections. A feedthrough post36 passes through lid 28 to stack 24 and is electrically insulated fromcase 20 and lid 28. Feedthrough post 36 is connected to a cathode tab35, while an anode tab 37 is directly attached between lid 28 and base26 such that the case itself acts as the anode terminal. In someembodiments, these roles are reversed and the cathode tab is connectedto the case and the anode tab connects to a feedthrough. In someembodiments, two feedthroughs are provided, one for the anode and onefor the cathode. Battery stack 24 is covered with insulating member 38when mounted within case 20. Other embodiments of insulating members,such as member 38, will be discussed below. In one embodiment, abackfill port 43 is located in the battery case. A backfill plug 41 andan optional cover 45 seal the backfill port after the battery case isfilled with electrolyte.

Battery stack 24 is constructed to provide optimal power storage in asmall space and allows for a battery having almost any arbitrary shapeor form factor. This allows battery 18 to be designed and dimensioned tofit within an implantable medical device, for example, and take up aslittle volume within the device as possible. In one embodiment, stack 24includes a plurality of alternating anode and cathode layers separatedby separators. As will be detailed below, these alternating electrodelayers are stacked, aligned, and interconnected to allow for maximalelectrode area in a minimal volume with minimal wasted space. Forexample, in one embodiment, battery 18 includes a layered stack ofelectrodes where the interconnections between layers are spread out soas to minimize the interconnection volume.

FIG. 2 illustrates an exploded view of battery stack 24 according to oneembodiment. Battery stack 24 includes an anode assembly including aplurality of anode sub-assemblies 100-100D and a cathode assemblyincluding a plurality of cathode sub-assemblies 300-300D, with separatorlayers 200 interposed between each of the sub-assembly layers. Thisflat, stacked, layered structure omits the wasted mandrel volume ofwound batteries and the wasted edge fold volume of folded batteries.Moreover, the flat, discrete layers allow the battery designer to makethe stack almost any shape desirable. This allows a medical devicedesigner to choose a battery which can accommodate a given space withinthe medical device.

One anode sub-assembly is a base, manifold anode collector layer 100which includes one or more tabs (A-E) extending from an edge of theanode layer body. Other anode sub-assembly layers in stack 24 includesecondary anode collectors 100A-100D, which each include an extensiontab, designated A-D, respectively. In this example, secondary anodesub-assembly collectors 100A each have a tab A which overlays and isaligned with base anode layer 100's tab A. In a likewise manner,secondary anode sub-assembly collectors 100B-100D each include anextension tab (B-D, respectively) which vertically matches or overlaysand aligns upon base layer 100 tabs B-D respectively. In thisembodiment, base layer 100 tab E includes tab 37 which connects theanode assembly to the battery case (FIG. 1). By spreading the anodeinterconnections to base layer 100 out over four separate areas, theoverall thickness required by the interconnections is lessened and lessspace is needed between stack 24 and case 20 (FIG. 1).

The cathode assembly of battery 24 includes a base, manifold cathodecollector layer 300 which includes one or more tabs (A-D) extending froman edge of the cathode layer body. Other cathode sub-assembly layers instack 24 include secondary cathode collectors 300A-300D, which eachinclude an extension tab, designated A-D, respectively. In this example,secondary cathode sub-assembly collectors 300A each have a tab A whichoverlays and is aligned with base cathode layer 300's tab A. In alikewise manner, secondary cathode sub-assembly collectors 300B-300Deach include an extension tab (B-D, respectively) which overlies andaligns upon base layer 300 tabs B-D respectively. In this embodiment,base layer 300 includes tab 35 which connects the cathode assembly tofeedthrough 36 (FIG. 1). Again, by spreading the cathodeinterconnections to base layer 300 out over four separate areas, theoverall thickness required by the interconnections is lessened and lessspace is needed between stack 24 and case 20 (FIG. 1).

Each separator 200 separates an anode sub-assembly 100-100D from acathode sub-assembly 300-300D. Each separator 200 includes a first edge251, a clearance area defined by a second edge 252, and a flat edge 253.The clearance area of separator 200 allows for interconnections to thefeedthrough. Separator 200 is, in one option, made from a roll or sheetof separator material. Suitable materials for the separator materialinclude, but are not limited to, a polyethylene, such as Tonen™, or atrilayer (polypropylene, polyethylene, polypropylene) separator materialsuch as Celgard™ 2325, for example. Other chemically inert materials aresuitable as well, such as porous polymeric materials. In one embodiment,each separator layer 200 is cut slightly larger than the anode layers(or cathode layers) to accommodate misalignment during the stacking oflayers, to prevent subsequent shorting between electrodes of oppositepolarity, and to act as an outermost edge for alignment.

FIGS. 3-8 show further details of an anode assembly of stack 24according to one embodiment. FIG. 3 shows an anode material 110. In thisexample anode 110 is a lithium (Li) anode. Each anode sub-assembly100-100D includes either one or two anodes 110 on the major surfaces ofthe sub-assembly. In various embodiments, the anode material 110 can bepressed into a mesh or etched base layer, or onto the surface of a baselayer, or be of pure Lithium and have no base layer. In one example, asheet of Lithium is attached to a base layer and then die cut to thedesired shape.

FIG. 4A shows base manifold anode collector layer 100. Collector layer100 includes an outer edge 130, a cut-out 132, an upper flat edge 134,and an edge 136. The base layer 100 also includes extension tabs A-E. Inone embodiment, each extension tab A-E is integral to layer 100. Someembodiments attach separate tabs A-E to layer 100. FIG. 4B shows adetail of base layer 100. In one embodiment, layer 100 is formed of amain body 120 including a stainless steel material, such as 316L SST, ora nickel material. A plurality of holes 125 are optionally incorporatedinto the stainless steel material. One or two anodes 110 (FIG. 3) areattached to the major surfaces of body 120. Tabs A-E (FIG. 4A) are notcovered with anode material. In one embodiment, the anodes can be formedby attaching strips of Lithium to one or both sides of strips ofstainless steel, leaving an edge open along a portion of the stainlesssteel strip for the tabs. One or more anode parts of desired shape arethen excised from the strip.

FIGS. 5-8 show anode sub-assemblies 100A-100D. Each of these secondaryanode layers includes an outer edge 130, a cut-out 132, an upper flatedge 134, and an edge 136 designated by the corresponding letters A-D inthe respective Figures. Each layer also includes a tab 140A-140D,respectively, with the tab of each separate layer being offset from theprevious and subsequent layers.

FIGS. 9-14 show further details of a cathode assembly according to oneembodiment. FIG. 9 shows an exploded view of a cathode sub-assemblyhaving a metal collector sheet 301 and a cathode material 310 on onemajor surface and a cathode material 312 on a second major surface. Inone embodiment, cathodes 310 and 312 are MnO₂ (manganese dioxide). Onemix ratio is about 90% MnO₂, 5% PTFE, and 5% carbon. Another embodimentprovides a mix ratio of 90% MnO₂, 5% binder, and 5% carbon or graphite.In one example, the cathode material can be a powder which is pressedinto a mesh base layer. In one embodiment, a cathode paste can beprovided which can be laminated, pressed, rolled, or otherwise mountedonto the surface of a base layer, as will be detailed below. In variousexamples, the cathode material can be a powder, paste, or adheredslurry.

FIG. 10 shows base manifold cathode collector 300. Collector 300includes an outer edge 330, cut-out 332 having tab 35 therein, and upperflat edge 334. Collector layer 300 also includes four extension tabsA-D.

FIG. 11A shows cathode sub-assembly secondary layer 300A having outeredge 330A, cut-out 332A, and flat edge 334A. A tab 340A extends fromedge 334A. FIG. 11B shows a detail of collector 300A. In thisembodiment, collector 300A is formed of a main body 320 including astainless steel sheet. A plurality of diamond structures 305 areincorporated into the main body by etching, an expanded metal process,by a mechanical process, or by laser, for example. One or two cathodes310 and 312 (FIG. 9) are attached to the major surfaces of body 320. Tab340A is not covered with cathode material. In one embodiment of formingthe cathodes, a layer of a paste or slurry is applied to one or bothsides of a stainless steel base layer, the strip is rolled or pressed tometer and attach the cathode material to the base layer, and then one ormore cathodes are excised from the strip. In one example, the cathodelayer is applied leaving the cathode tabs bare.

FIGS. 12-14 show secondary cathode sub-assembly layers 300B-300D,respectively. Each secondary cathode layer includes an outer edge 330,cut-out 332 and upper flat edge 334 shown by the corresponding lettersB-D in the respective Figures. Each layer also includes a tab 340B-340D,respectively, with the tab of each separate layer being offset from theprevious and subsequent layers.

Again, each anode tab 140A-140D and each cathode tab 340A-340Dcorresponds to a tab A-D on either the base anode layer 100 or the basecathode layer 300.

Also, these spread out interconnections of the anodes and cathodesdecrease the overall thickness of the space between the stack and thecase, allowing for a smaller battery size. To ensure that a batterystack takes up as little volume as possible and to optimize theconsistency between each battery being manufactured, it is important tocarefully align each layer of the battery stack when constructing thestack. In one embodiment, battery stack 24 described above is alignedusing an alignment fixture to provide for optimal surface area of thebattery.

FIG. 15 illustrates an alignment mechanism or fixture 400 used toassemble battery stack 24, in accordance with one embodiment. Alignmentmechanism 400 includes a plurality of precisely placed alignmentelements 501-504. Alignment elements 501-504 are vertically orientedalignment elements which extend from a base 402. Base 402 supportsbattery components thereon, while the alignment elements 501-504 alignthe battery layers while the layers are being stacked therein.

FIGS. 16-17 shows one example use of alignment fixture 400. FIG. 16shows a perspective view of stack 24 within the fixture and FIG. 17illustrates a top view of battery stack 24 within fixture 400. Batterystack 24 includes a plurality of discrete electrode layers with eachlayer aligned relative to the position of the alignment elements501-504. A channel can be provided in base 402 to hold a fastener forwrapping around a portion of the battery stack 24 once it has beenstacked and aligned. In one example, a tool can be inserted into thechannel to clamp the stack and remove it for taping. Precise alignmentof battery stack 24 is maintained by the alignment elements 501-504 whenwrapping the battery stack 24.

In one example, to align the layers of battery stack 24, a separatorlayer 200 is attached to each respective electrode layer of the stack.The separators 200 can dimensioned such that they slightly overhang theedges of each electrode layer. Each layer is then placed betweenalignment elements 501-504. One or more points on the outer perimeteredges (251-253, etc.) of each separator layer abut against each of theelements 501-504, precisely aligning that layer. This technique helps toreduce variances in alignment which may result from varying tolerancestack ups between layers of the assembly and the alignment fixture used.Moreover, by using the outer edges, no area within the body of eachlayer is wasted by using alignment holes, for example.

In one embodiment, each separator layer 200 is aligned relative to theplurality of alignment elements 501-504 by placing the separator so thatouter edge 251 and edge 253 extend to contact the alignment elements501, 502, 503, and 504. In one example, the separator layer 200 is thenattached to an anode assembly 100-100D or a cathode assembly 300-300Dwhile the separator is positioned within the fixture. These sub-assemblylayers are then put one by one into fixture 400 between elements501-504. The edges of the separators 200 contact the elements 501-504and align the electrode layers.

In one embodiment, each sub-layer or series of sub-layers are pressed tohelp reduce warpage and thus to reduce the overall height of the batterystack 24. A fastener 351 (FIG. 21) can be wrapped around a portion ofthe stack 24 to retain the alignment of the layers relative to oneanother. In one embodiment, the fastener includes a tape that is wrappedaround a central portion of the battery stack 24. The battery stack 24can then be clamped and annealed.

In some embodiments, the anode sub-assembly layers 100-100D and thecathode sub-assembly layers 300-300D are aligned relative to one anotherwithin case 20, instead of using the external alignment mechanism 400,and then are coupled to one another in the aligned position. Forinstance, an outer edge of a separator of the anode sub-assembly and anouter edge of a separator of a cathode sub-assembly can contact aninterior surface of the case 20, and would be aligned therein.

Among other advantages, use of the alignment fixture described aboveprovides for a battery making efficient use of space within the case,permits increased anodic and cathodic surface area, and increasedcapacity for a battery of a given set of dimensions. Variation in theouter dimensions of one battery stack 24 to another battery stack 24 isreduced because each is formed within alignment elements positioned thesame manner. Moreover, dimensional variations in the battery stackresulting from variation in the reference points from case to case oralignment apparatus to alignment apparatus are eliminated. This providesimproved dimensional consistency in production and allows for reducedtolerances between the battery stack and the battery case. This allowsfor more efficient use of space internal to the battery case.

Furthermore, multiple points can be used to make the alignment, reducingthe effect of the tolerance stack up between the conductive layer orseparator being aligned and the alignment element at any one position.This also facilitates for alignment of components which during certainsteps in the manufacturing process have portions which extend beyond thedimensions defined by the case and are later formed to fit within thecase.

The battery stack structure described above provides for greatercathodic/anodic surface area since, by aligning to the separator, thecathode/anode surface area is optimized by not having to provideextraneous alignment notches or other alignment features within or onthe electrodes themselves which decrease the electrode surface area.However, in some embodiments, one or more features, such as holes ornotches can be provided in the surface of each of cathode assembly300-300D, anode assemblies 100-100D, and separators 200 allowing forinternal alignment of the stack. For example, fixture 400 can include acentral post and each layer is mounted over the central post such thateach layer is registered.

FIG. 18A shows a sectional side view of an alignment mechanism 600 forforming a battery stack according to one embodiment. Alignment mechanism600 generally includes a base 610, a base pad 620, and first and secondupper members 634 and 636. In use, fixture 600 helps to continually keepall the layers of a battery stack 624 in compression as the batterystack is being formed. In one embodiment, as will be detailed below, aseach separate layer of the battery stack is placed upon base pad 620,the base pad urges the stack upward while upper members 634 and 636provide a holding, downward force on the stack such that the stack issqueezed between base pad 620 and upper members 634 and 636. Thissqueezing or compression holds each layer of the battery stack in theposition in which it was placed on the stack, thus keeping the alignmentof the battery stack.

Base 610 includes an interior cavity 640. In one embodiment, interiorcavity 640 is shaped to accommodate base pad 620 therein to allow thebase pad to translate up and down. Base pad 620 and cavity 640 areshaped to accommodate example battery stack 624 As noted above, flatbatteries can be formed into almost any shape. Accordingly, base pad 620can have almost any shape.

Base pad 620 includes a flat top surface for supporting a bottom surfaceof battery stack 624. In one embodiment, the surface area of the basepad surface is slightly larger than the surface area of the batterystack. In one embodiment, a straight, longitudinal groove 627 isprovided in the top surface of base pad 620. Along with a correspondinggroove in base pad 610, groove 627 provides a space for a binder such asa tape to be laid into while a battery stack is being formed in fixture600. After the stack is formed, the tape can be wrapped around thebattery stack to bind the stack and to hold the stack's alignment.Groove 627 can also be used as a stack picking feature. For example, atool can be inserted into the channel of groove 627 to clamp the stackand remove it for taping. Some embodiments omit groove 627.

Fixture 600 includes one or more forcing or biasing members such assprings 626 which are located beneath base pad 620 to urge base pad 620upward. In use, the spring force grows as the stack is formed until theforce is approximately 2 lbs. when the base pad is fully depressed. Inother examples, the high end force can range from ¼ lb. to approximately3 lbs., approximately 4 lbs., or more, depending on the material beingstacked. Also, the low-end force (i.e., when the stack is empty) can bevaried. For example, a pre-load can be applied on the springs to urgethe base pad against the bottom of members 634 and 636 before anybattery layers have been placed therein. This pre-load force can rangefrom zero, less than approximately ¼ lb to approximately ¼ lb.,approximately ½ lb., or more, depending on the application. In oneembodiment, the spring is omitted and a pressurized air dashpotmechanism is located under base pad 620 to urge the base pad upward. Thepressurized air mechanism can have adjustable air pressure settings, andallow for a constant upward force on the base pad.

In one embodiment, each upper member 634 and 636 is a thin, flat member,such as a metal strip or a plastic strip. In this example, the uppermembers 634 and 636 are located so as to contact the top side edges ofthe battery stack when the stack is being formed. This helps keep theedges of a given layer from curling up. This helps prevent misalignmentof the stack since any deviation from flatness can be a cause ofmisalignment.

In one example use, a robotically controlled vacuum placement arm 660places each new layer 624X on top of the previous layer. Someembodiments provide manual placement of each layer. A vision alignmentsystem can be used to align the layers. Upper members 634 and 636 aremovably attached to the fixture so that they can rotate off and on thestack. For example, uppers members 634 and 636 are moved out of the waywhen a new layer is being place on the stack and arm 660 holds the stackin compression. After the new layer is placed correctly the members 634and 636 move back over the edges of the top of the stack and the arm 660is removed and the arms then hold the stack in compression. This processis then repeated until the stack is formed.

Fixture 600 allows for precise alignment of a battery stack which has acurved or non-uniform profile (See FIGS. 21 and 22 for example, wherethe upper and lower portions of stack 24 are smaller in area than themiddle portion, resulting in a curved profile battery stack). In such acurved profile battery stack, the edges are not uniform so as to provideprecise alignment when stacking in a fixture such as fixture 400.However, by squeezing the stack, fixture 600 allows for precisealignment regardless of the edge profile of the stack.

Further details of some embodiments of alignment mechanism 600 arediscussed in co-pending and co-assigned U.S. application Ser. No.10/050,598 (filed Jan. 15, 2002) entitled METHOD OF CONSTRUCTING ACAPACITOR STACK FOR A FLAT CAPACITOR, which is incorporated herein byreference in its entirety.

FIGS. 18B-18F show a stacking fixture 670 according to one embodiment.Stacking fixture 670 includes some similar features as discussed abovefor fixture 600 and certain details will be omitted for sake of brevity.Fixture 670 includes a base 672 to hold a stack as the stack is beingbuilt layer by layer. One embodiment includes springs or other forcingmembers (such as an air pressure dashpot mechanism, as discussed above)under base 672 to urge the base and the battery stack upwards (asdiscussed above for fixture 600). Fixture 670 includes a placementmember 671B to deliver each anode, cathode, or separator layer to thestack. In some embodiments, placement member 671B can include manualplacement members, vacuum placement members, robotically controlledplacement members, vision alignment systems and so on as discussedabove. In one embodiment, an upper clamping member 671A is rotatablycoupled to fixture 670 to apply top pressure on the stack when uppermembers 673 and 674 are moved away and placement member 671B is movedaway. Other embodiments omit member 671A and utilize the techniquedescribed below. A groove or channel can be provided in the upperportion of the base 672 to allow for a tape strip or a tool to beinserted to remove the stack from the fixture.

Fixture 670 includes upper members 673 and 674 which are situated onopposite sides of the stack. Each upper member 673 and 674 includes acontacting member 675 and 676, respectively. Each of the contactingmembers 675 and 676 is held in tension and supported by being mounted toarms 680 and 681 at each of the contacting members ends. Contactingmembers 675 and 676 contact the top surface of the top layer of thebattery stack as it is being built. The compression or holding forcebetween the contact members 675 and 676 and the base pad 672 keeps thebattery stack in alignment as the stack is being built layer by layer.

FIG. 18C shows a view of contacting members extending across a topsurface of a top layer 677 of a battery stack 678. It is noted that thebattery stack can be oriented in any manner desirable (e.g. the stackcan be turned 90 degrees relative to FIG. 18C). FIG. 18D shows oneembodiment of a contacting member 675B. Contacting member 675B includesa thin strip of plastic, such as a mylar, polyethelyne, or polypropylenefilm web, for example. Various embodiments have contacting membershaving a thickness of approximately 0.001 inches or less, toapproximately 0.005 inches. This end-supported thin web of material isstronger and better supported than a cantilevered member and thethinness of the material allows for a minimal deflection of each newlayer as it is put on top of the stack.

FIG. 18E show a contacting member 675C which includes a roll of thinplastic material. In this example, the web of member 675C can be indexedand drawn through arms 680 and 681 every one or more times it is used.This can provide clean material for contacting the battery stack andallow the web to maintain its strength.

FIG. 18F shows an example use of fixture 670 in placing top layer 677onto a battery stack 678. In this example each layer of the batterystack is aligned and placed upon the stack which rests on base pad 672.Only contacting member 675 is shown in FIG. 18F for sake of clarity. Inone embodiment, second contacting member 676 is used on the oppositeside of the stack as shown in FIG. 18B.

In use, placement member 671B places layer 677 on top of the stack andholds the layer as originally aligned in place on top of the stack. Insuch a position the edge of layer 677 is then on top of contactingmember 675. Contacting member 675 is then moved outward to position 1,upward to position 2 then back to positions 3 and 4 where the bottom ofcontacting member 675 then contacts and holds layer 677 down upon stack678. Placement member 671B then moves away to get the next layer withcontacting member 675 (and 676) holding the stack in alignment. Thisprocess is then continued until the battery stack is formed, with member671B and members 675 and 676 alternating keeping the stack incompression.

As with fixture 600, fixture 670 allows for precise alignment of abattery stack which has a curved or non-uniform profile (See FIGS. 21and 22). In such a stack, the edges are not uniform so as to provideprecise alignment when stacking in a fixture such as fixture 400.However, by squeezing or at least holding the stack still, fixture 670allows for precise alignment regardless of the edge profile of the stacksince the stack never has the opportunity to shift once a layer isaligned and placed onto the stack. Moreover, thin contacting members 675and 676 provide for the minimal deflection of the layer when they moveaway from the stack. For example, FIG. 18G shows how each top layer 677is deflected by contacting member 675 as it is being placed on stack 678by the placement member. By providing a thin contacting member, thisdeflection can be minimized.

In some embodiments, the edges of the cathode layers and anode layers ofthe battery stack 24 described above are generally co-extensive oraligned with each other within stack 24. In other embodiments, a batterystack can include anode and cathode layers having at least partiallyoffset edges.

For example, FIGS. 19 and 20 show top and side views of a battery stack724 according to one embodiment. Battery stack 724 includes an anodelayer 701, a separator 702, and a cathode layer 703 that are configuredin a layered structure analogous to battery stack 24 described above.The bottom surface in FIG. 19 is the cathode layer, and the top surfaceis the anode layer with the separator interposed there between. In oneembodiment, separator 702 can extend beyond both anode layer 701 andcathode layer 703.

Some cutting and punch-die processes used to make anode and cathodebattery layers can produce burrs on the layers that can result in ashort circuit if a burr on an anode layer edge portion makes contactwith an adjacent cathode layer or vice-versa. When the dimensions of thecathode and anode layers are the same so that the edges of each layerare aligned, a burr on a cathode layer edge portion can then contact aburr on an anode layer edge portion. Burrs on overlapping edge portionsof the anode and cathode layers may then make contact and cause a shortcircuit by traversing only half of the thickness of the separatorbetween the two layers.

Accordingly, in one embodiment, the battery stack is constructed withlayers having edge portions that are offset from one another. In oneembodiment, this is done by having a cathode layer with a differentdimension than the anode layer so that portions of their edges areoffset in the layered structure (i.e., either the anode layer or thecathode layer is smaller than the other). The anode and cathode layersmay be of the same general shape, for example, but of different surfaceareas so that the perimeter of one layer is circumscribed by theperimeter of the other layer.

The capacity of a lithium-based battery is determined by the amount ofcathode material (such as MnO₂) that can safely be packaged in thedevice. Also, it can be desirable to have the anode fully opposed by thecathode. Accordingly, altering the surface area of the anode layer doesnot appreciably affect the capacity of the device. Such an arrangementis shown in FIGS. 19 and 20 where the anode layer 701 is of the samegeneral shape as the cathode layer 703 but with a smaller surface areasuch that the edge portions of the anode layer are inwardly offset fromthe cathode layer edges. In this structure, only an edge burr on theanode layer that traverses the entire thickness of the separator canproduce a short circuit. This is in contrast to the case where the edgeportions of the two layers are aligned rather than being offset.Offsetting the edge portions results in a greater tolerance for edgeburrs and allows a less constrained manufacturing process and a thinnerseparator to be used.

Battery stack 724 can include a plurality of electrode elements that arestacked on one another with each electrode element being a layeredstructure such as shown in FIG. 19. The anode layers 701 are stacked oncathode layers 703 in alternate fashion with separator 702 interposedbetween each anode layer and each cathode layer.

In one embodiment, the offset structure described above can beincorporated into a cylindrical battery. For instance, the anode andcathode layers are cut from a sheet in a desired width and length. Theanode layer is made narrower than the cathode layer so that the edges ofthe anode layer are inwardly offset from the cathode layer edges. Thecylinder configuration is then produced by rolling the layers intoconcentric anode and cathode layers that are separated by separators.

Offsetting of anode layer and cathode layer edge portions may beaccomplished by using a variety of differently shaped and/or dimensionedcathode or anode layers.

In one embodiment, for example, a battery used in implantabledefibrillators and designed to operate at a rated voltage ofapproximately 2.75 volts to 3.4 volts, includes a ratio of the anodelayer surface area to the cathode layer surface area of approximately1.2 or greater. In some embodiments, the ratio is approximately 1.3 toapproximately 1.4. In various embodiments of the present system, a ratioof Li/MnO₂ capacity can vary between approximately 0.85 to 1.7.

Referring again to FIG. 16, once stack 24 is stacked as shown, the anodesub-assembly layers are interconnected via anode tabs A-D and thecathode sub-assembly layers are interconnected via cathode tabs A-D. Theinterconnections can be made by welding, staking, or other techniques.Each tab of the various electrode layers is electrically coupled to theother tabs through base manifold layer 100 or 300. Each secondaryelectrode layer has at least one extension tab positioned to overlay, beco-extensive with, or match with one of the plurality of tab positionsA-D.

In this embodiment, the cathode layers are positioned to include fourtab groups 350A-350D. Similarly, anode layers are positioned to includefour anode tab groups 150A-150D. The tab groups are in electricalcontact with each other through the base layer 100 or 300. Thus, eachcathode layer is electrically connected to tab 35 and finally throughthe feedthrough 36, and each anode layer is connected to tab 37 and thento the case.

In other words, from a top view perspective, anode tabs A-D and cathodetabs A-D are commonly positioned or co-extensive with anode and cathodebase tabs A-D respectively.

The base tabs and matching secondary tabs may be separate membersattached or welded to the metal sheets or the tabs may be integral withthe foil layer. The base anodes and cathodes are shown with four tabsand the secondary electrodes are shown with one tab, however, any numberof tabs can be provided as needed. In some embodiments, the secondarylayers include two or more tabs to create redundancy.

Again, since the extension tabs are spread out, the size needed to fitthe stack within the battery case is reduced. Moreover, the integralinterconnects provide for a reduced resistance of the interconnections.This results in an optimized maximal battery surface area per unitvolume of the battery. Moreover, the battery then has reduced impedancedue to the integral interconnects. For example, because the battery hasan interconnect at each layer, it is in effect a multi-parallelinterconnection scheme that has lower impedance than that of a rolled orfolded battery with only one or two tabs.

In one embodiment, battery stack 24 includes the matching tabs of eachsecondary layer group welded to the corresponding tab of the base layer.These groups are folded against the battery stack, forming the anode tabgroups 150A-150D and cathode tab groups 350A-350D. Again, tab groups350A-350D electrically connect to an external cathode connection via tab35 which provides an external electrical connection. Tab groups150A-150D electrically connect to tab 37.

In this embodiment, tab groups 150A-150D and 350A-350D are folded intoposition on a top surface 32 of battery stack 24. The tab groups arefolded onto the top of the stack and taped. Alternatively, the tabgroups are cut just beyond the weld and taped against a face 30 of thestack (See FIG. 21). Each tab group 150A-150D and 350A-350D has athickness that is less than the sum of the base layer and all thesecondary layers.

In one example, the thickness of the tab groups are approximately equalto or less than the space between the main body of stack 24 and lid 28of case 20 (FIG. 1). In some embodiments, the space is merely aline-to-line interference fit. The present cathode and anode structureprovides that the cathode interconnections and anode interconnectionsfit within the limited room available.

For example, in one or more of the embodiments described above theelectrode interconnects are spread out or distributed over multiplelocations. For example, the cathode or anode layers can be spread outover four locations with four tab groups, with the thickness of each tabgroup at each location being about 0.006 inch after welding (assumingthat four layers at 0.001 inch per layer are at each location). Thisthinness of the tab group allows the stacked unit to be placed into thehousing with the tab groups occupying the space between the housing andthe edge of the stack or the clearance space between the lid and the topof the stack. These clearance spaces are allowed for inserting the stackinto the housing. As a comparison, if the cathode tabs were all broughtout at one location, the thickness would be greater than 0.015 inch andmake it difficult, if not practically impossible, to fold the tabscollectively over the stack as in FIG. 21. Thus, this thickness wouldrequire that part of the stack be removed or the case enlarged to allowspace for routing and connecting the cathode layer connections, therebyreducing the packing efficiency of the battery.

The embodiment described above show the base layer and secondary layeras cathode and anode layers. However, in some examples only the anode orthe cathode layer is arranged in the present fashion and the other isarranged in a different manner.

FIG. 22A shows front view of stack 24 of FIG. 21. Here it can be seenthat in one embodiment, the present system allows for the use ofnon-uniform layers of a battery. In this example, generally designatedare a top stack portion 24A, a middle stack portion 24B and a bottomstack portion 24C. Each of the stack portions 24A-24C includes one ormore cathode layers, separator layers, and anode layers. The layers oftop portion 24A have at least one dimension which is smaller than thesimilar layers in middle stack portion 24B. Likewise, bottom stackportion 24C includes at least one dimension smaller than similar layersin middle stack portion 24B. This dimensional difference results in thecurved profile of stack 24.

Portions 24A-24C are staggered so that their perimeter edges generally(or at least a portion of a side of the stack) define a profile thatgenerally conforms or is substantially congruent to an adjacent curvedinterior portion of battery case 20 (FIG. 1) without wasting any spacewithin the case. FIG. 21 shows that portions 24A-24C can be staggered intwo dimensions. As discussed above, fixture 600 (FIG. 18) can be used toform the curved or staggered profile stack 24.

In various embodiments, stack 24 can have a variety of profiles and canbe curved along zero, 1, 2, 3, or more sides of the battery. The stackcan be curved along a top portion, a bottom portion, or both.

Thus, the curved profile stack allows for a curved profile battery case(FIG. 1). This advantageously takes advantage of an implantable medicaldevice housing, which can include a curved outer surface and a curvedinner surface. Thus, the present shape provides an optimal amount ofbattery power packaged in a way that takes advantage of the preferredshape of an implantable medical device. This allows the battery stack 24to fit tightly within a curved case with as little wasted space aspossible. A curved case is usually a better fit within an implantablemedical device. Thus, this structure allows for a smaller medical devicewithout lowering the available energy of the battery by increasing thevolumetric and gravimetric energy density of the battery.

FIG. 22B is a perspective view of an insulating sheath or insulatingmember 50 according to one embodiment and FIG. 22C is a side view ofinsulating member 50. In this example, insulating member 50 is shapedand dimensioned to hold a battery stack shaped as battery stack 24(FIGS. 1 and 21), for example. Other embodiments can shape insulatingmember 50 as needed to conform to and cover the outer surfaces of abattery stack. In one embodiment, insulating member 50 is used in placeof insulating member 38 (FIG. 1) to insulate the battery stack from case20.

In one embodiment, insulating member 50 includes a main insulating body52 which defines a cup shape and includes a top surface 61 and anopposing bottom surface 62 and having an opening 54 along a side of thebody. One or more flaps 55 and 56 extend from an edge of opening 54.Flaps 55 and 56 are dimensioned to fold over and cover opening 54 aftera battery stack has been inserted into main body 52. In one embodiment,a first flap portion 57 covers the exposed surface of the battery stackand a second flap portion 58 can be attached to the top surface of mainbody 52. Thus, a battery stack, such as stack 24, can be insertedthrough opening 54 into the hollow area within main body 52. Flaps 55and 56 are folded over the exposed portion of the stack and the batterystack is separated from and insulated from the battery case. One or moregaps or spaces 59 and 60 can be provided between or adjacent to flaps 55and 56 to provide room for extension tabs 37 and 35 (FIG. 1) to extendfrom the stack.

In one embodiment, flaps 55 and 56 are integrally formed with body 52.This integral structure allows for more efficient use of insulatingmember 50 during manufacturing than a two or more part construction.Integral flaps provide for cost savings in both piece part andmanufacturing assembly. Moreover, the integral structure of insulatingmember 50 reduces the volumetric inefficiencies of two part insulatorssince the present structure reduces or eliminates any overlap region ofthe insulating structure when it is mounted around the battery stack.For example, only a single, top seam results when the edge of flaps 55and 56 meet top surface 61.

FIG. 23A shows a side view of battery stack 24 and battery case lid 28.Feedthrough 36 extends through a feedthrough hole 45 in lid 28 and isconnected to tab 35. FIG. 23B shows a cross-section of the connection.Tab 35 wraps around feedthrough 36 and is attached at section 35X. Thisallows for a stress-relief area of the tab attachment.

FIG. 23C shows a cross-section of the feedthrough assembly 40 of battery18. Feedthrough assembly 40 includes a ferrule portion 42 integrallyfashioned from a wall 43 of lid 28. In other embodiments, the ferrulemember can be fashioned from the base 26 of case 20. Ferrule portion 42includes an integrally formed annular structure defining feedthroughhole 45 which has an inward facing cylindrical surface 45S. An annularinsulating member 44 is located within ferrule portion 42. In oneembodiment, annular insulating member 44 can be a glass member, an epoxymember, a ceramic member, or a composite member, for example. In oneembodiment, annular member 44 includes a TA23 glass or equivalent glass.Feedthrough post 36 extends through annular member 44. Feedthrough post36 can include a molybdenum material. Annular member 44 electricallyinsulates feedthrough 36 from lid 28 and provides a hermetic seal ofbattery 18.

Annular member 44 has an outer surface abutting inward facingcylindrical surface 45S. Annular member 44 includes an inner hole 48.Feedthrough post 36 extends through inner hole 48 and is glassed intothe battery case. This allows the feedthrough post to have one endconnected to a portion of the electrode assembly, such as cathode tab35, and a second end expose externally to the housing to provide acathode terminal for the battery. The integral ferrule structureprovides ease of manufacturing a battery since the ferrule does not needto be welded onto the case. Moreover, it can be a cost-effective andsize advantageous approach for a hermetically sealed battery. Byinstalling the feedthrough directly into the feedthrough hole in thecase, a difficult welding step is eliminated since the case and thefeedthrough ferrule are a combined assembly rather that two separatesubassemblies that need to be joined together.

FIG. 24A shows a side view of battery 18 after the battery has beenassembled. FIG. 24B shows a cross-section of battery 18, and FIG. 24Cshows a close-up detail of the cross-section of FIG. 24B. Here it can beseen that by staggering the tab connections of the present embodiment. Aspace 60 between stack 24 and lid 28 can be small to allow for anoptimal use of space within the battery case.

FIG. 25 shows a battery assembly 800 according to one embodiment andFIG. 26A shows an exploded view of battery 800. Battery 800 can beconstructed using some features and techniques discussed above and theabove discussion is incorporated herein by reference. Battery 800 is aflat, stacked battery having a non-rectangular shape. Again, thetechniques described above and below allow the manufacture of almost anyarbitrarily shaped battery to allow a designer to fit the battery in agiven space within an implantable medical device, for example. A batterystack 814 is mounted within a battery case 802. In one embodiment, case802 is a two-part clamshell case having a first part 803 and a secondpart 804. Case 802 can be a metallic case manufactured from a conductivematerial, such as stainless steel. In another option, case 802 ismanufactured using a nonconductive material, such as a ceramic or aplastic.

Battery stack 814 has a region 815 at its periphery which is indentedrelative to the shape of case 802. This indented region 815 ispositioned when the stack 814 is installed in case 802 to provide spacefor electrical connections. A feedthrough post 808 passes through case802 to stack 814 and is electrically insulated from case 802.Feedthrough post 808 is connected to a cathode tab 824, while an anodetab 822 is directly attached to case 802. An anode terminal 810 isconnected to the outer surface of case 802. In some embodiments, theseroles are reversed and the cathode tab is connected to the case and theanode tab connects to a feedthrough. In some embodiments, twofeedthroughs are provided, one for the anode and one for the cathode.Battery stack 814 is wrapped by a strip of tape 828 to help hold thestack together and in alignment. Stack 814 is covered with one or moreinsulating members 811 and 812 when mounted within case 802. In otherembodiments, other insulating members, such as the one-piece integralinsulating member discussed above can also be used. A backfill port 806is provided in the case. In one embodiment, an annular insulating member827 is positioned beneath and around a feedthrough ferrule (see alsoFIG. 47A) to prevent any short circuits between interconnect 824 and thecase. Insulating member 827 also helps minimize galvanic corrosionpotential. One example material for member 827 is a polyethylenematerial.

First part 803 of clamshell case 802 includes a lip 825 which isindented to allow edge 826 of second part 804 to matingly mount aroundlip 825.

Battery stack 814 is constructed to provide optimal power storage in asmall space. This allows battery 800 to be dimensioned to fit within animplantable medical device, for example, and take up as little volumewithin the device as possible. In one embodiment, stack 814 includes aplurality of alternating anode and cathode layers separated byseparators. As will be detailed below, these alternating electrodelayers are stacked, aligned, and interconnected to allow for maximalelectrode area in a minimal volume with no wasted space.

In one embodiment, stack 814 can include one or more staggered portionsor profiles. For example, stack 814 can include non-uniform anode orcathode layers. Stack 814 includes a top portion 820, a middle portion818 and a bottom portion 816. Each of the stack portions 816-820includes one or more cathode layers, separator layers, and anode layers.In one embodiment, the layers of top portion 820 have at least onedimension which is smaller than the similar layers in middle stackportion 818. Likewise, bottom stack portion 816 includes at least onedimension smaller than similar layers in middle stack portion 818. Thisdimensional difference results in the curved profile of stack 814.

Portions 816-820 are staggered so that their perimeter edges generally(or at least a portion of side of the stack) define a profile thatgenerally conforms or is substantially congruent to an adjacent curvedinterior portion of battery case 802. In various embodiments, stack 814can have a variety of profiles and can be curved along zero, 1, 2, 3, ormore sides of the battery. The stack can be curved along a top portion,a bottom portion, or both.

Thus, the curved profile stack 814 allows for a curved profile batterycase 802. This takes advantage of an implantable medical device housing,which can include a curved outer surface and a curved inner surface.Thus, the present shape provides an optimal amount of battery powerpackaged in a way which takes advantage of the preferred shape of animplantable medical device. This allows the battery stack 814 to fittightly within a curved case with as little wasted space as possible. Acurved case is usually a better fit within an implantable medicaldevice. Thus, this structure allows for a smaller medical device without lowering the power of the battery. (See FIG. 22A and accompanyingdiscussion for other details).

FIG. 26B shows battery stack 814 according to one embodiment. In thisexample, insulating members 811 and 812 (FIG. 26A) are omitted and stack814 is insulated by wrapping the peripheral edge of the stack with aninsulating member such as an insulating strip 811B. In one embodiment,strip 811B includes a strip of polyimide tape wrapped twice around theedge of the stack. Two wraps provides for increased heat resistancealong the weld line of the battery case 803, 804 (FIG. 26A) and theability to manage variations in the height of the battery stack. In thisexample, the top and bottom surfaces of stack 814 do not need to beinsulated from the battery case because they are the same electricalpotential as the case. This design also improves the packaging densityof battery 802.

FIG. 27 shows an exploded view of battery stack 814 according to oneembodiment. Battery stack 814 includes an anode assembly including aplurality of anode sub-assemblies 840, 842, and 844 and a cathodeassembly including a plurality of cathode sub-assemblies 841 and 843.Anode sub-assemblies 840 and 844, located near the top and bottom ofstack 814, are smaller than the other anode assemblies, and cathodesub-assemblies 841 are smaller than the other cathode sub-assemblies toaccommodate a curved battery case edge. In this example, anodes 840 and844 have lithium attached to a single side of the anode. Each anodesub-assembly includes a tab extending from the body of the anode at alocation A. Each cathode sub-assembly includes a tab extending from thebody of the cathode at a location B. To form stack 814, a stackingfixture such as those discussed above can be used, such as fixtures 600or 670, for example. After stacking, the anode tabs are brought togetherand welded to connect each of the anode layers into an anode assembly.Likewise all of the cathode tabs are brought together and welded to forma cathode assembly.

In some embodiments, the anode and cathode layers of stack 814 areseparated by separator as discussed above. In other embodiments, each ofthe cathode sub-assemblies 841 and 843 includes a heat-sealed separator846 which is formed to substantially surround, encapsulate, or envelopthe cathode member of the sub-assembly while allowing the extension tabof the cathode to be open.

FIGS. 28, 29, 30, and 31 show one embodiment of an encapsulated cathodeassembly 843. (The present encapsulation technique is also applicable tothe anodes discussed herein.) FIG. 28 shows a top view of cathodesub-assembly 843 which includes a cathode 853 sandwiched between twolayers of separator material 847 with one layer of separator material oneither side of the cathode. In one embodiment the separator material ispolyethylene, such as Tonen™, or a trilayer (polypropylene,polyethylene, polypropylene) separator material such as Celgard™ 2325.

To form the encapsulated cathode assembly 843, the region periphery 848,just outside the outer edge of the cathode is sealed to attach the twolayers of the separator 847 together and thus encapsulate the cathode853 between the separators 847. One technique of sealing the layersincludes heat sealing. This can include a thin line heat sealed aroundthe entire periphery as shown as region 848 in FIG. 28. In this example,the entire periphery of the cathode is encapsulated within the separatorenvelope except for the lead 849. In one example, the heat sealingprocess also cuts the sealed cathode sub-assembly 843 from the web. Insome embodiments, the encapsulation process includes ultrasonic welding,ultrasonic sealing, hot die sealing, or inductive sealing the separatorstogether along the periphery of the cathode to form the encapsulatedcathode sub-assembly.

When encapsulated, cathode 853 is constrained within the separatorenvelope-like structure such that cathode 853 does not shift whensub-assembly 843 is grabbed by the separator material 847. This savestime in manufacturing. For example, instead of stacking and carefullyaligning an anode, a separator, and a cathode, the stacking operationincludes stacking and aligning an anode and an encapsulated cathodeassembly 843. This saves manufacturing time and makes alignment simplersince each separator does not have to be aligned with each anode andeach cathode since the separator is automatically aligned during theencapsulation process. In other words, it cuts the number of individualpieces to be stacked in half.

FIG. 30 shows a detail of the tab portion of the encapsulated cathodesub-assembly 843. The cathode 853 include a base layer 851 havingcathode material 852 pressed or otherwise mounted onto one or both sidesof the base layer. The two separator layers 847 are sealed at region 850with tab 849 extending from the sealed region.

FIG. 31 shows a detail of a bottom portion of the encapsulated cathodesub-assembly 843. The sealed region 848 of separator layers 847 forms aflange 851 around the periphery of the encapsulated assembly 843. Flange847, which extends around the periphery of the cathode sub-assembly (SeeFIG. 28), offers shorting protection around the entire periphery of thecathode rather then just the main surfaces of the cathode as when asingle separator layer is placed between each cathode and each anodelayer. Moreover, the encapsulated structure prevents any flaking cathodematerial from floating around the cell once constructed.

In one embodiment, stack 814 is formed using the anodes and cathodesshown in FIGS. 32-33. FIGS. 32-36 show a cathode and anodeinterconnection technique according to one embodiment. FIG. 32 shows acathode 860 having a cathode material 861 mounted upon a base layer andan uncoated connection portion or tab portion 862 having a proximalportion 863 connected to the main body of cathode 860 and a distalportion 864 extending therefrom. FIG. 33 shows an anode 865 having ananode material 866 mounted upon a base layer and an uncoated connectionportion or tab portion 867 having a proximal portion 868 connected tothe main body of anode 865 and a distal portion 869 extending therefrom.In one embodiment, connection members 862 and 867 include one or moreseparate members attached to the anode or cathode by welding, staking,or other connection method. In other embodiments, connection members 862and 867 can be integral portions of the anode or the cathode, and can bepunched, laser-cut, or otherwise shaped from the base layers.

In one embodiment, an additional layer of material is provided on eitheror both of connection members 862 and 867 to give them a thicknessapproximately equal to or slightly larger than the thickness of eithercathode 860 or anode 865. This extra material minimizes the movement ofthe connection members when they are squeezed together. A similarstructure is discussed below for FIG. 36B, the discussion of which isincorporated herein by reference.

FIG. 34 shows a separator according to one embodiment. Separator 870includes a cut-out region 873 which allows the connection members 862and 867 to extend beyond the separator. In some embodiments, a discreteseparator is omitted and cathode 860 can be encapsulated within aseparator envelop or bag, such as discussed above.

FIG. 35 shows a top view of a battery stack 871 including alternatinglayers of anodes 865, separators 870 and cathodes 860. In stack 871,connection members 862 and 867 are overlaying and underlying each other.As used herein, overlay and underlay refer to the position or locationof portions of the cathodes and anodes which are commonly positionedfrom a top view. In the embodiment of FIG. 35, it is seen thatconnection members 862 and 867 have some commonly positioned portionsrelative to each other and some portions which are exclusivelypositioned relative to each other.

For instance, proximal sections 868 and 863 are exclusively positionedor located. This means that at least a portion of proximal sections 868and 863 do not overlay or underlay a portion of the proximal sections ofthe other proximal section. Conversely, distal sections 864 and 869 arecommonly positioned and each include at least a portion overlaying orunderlaying each another.

When stacked as shown in FIG. 35, the edges of distal sections 864 and869 form a surface 874. This surface 874 provides for ease ofedge-welding or otherwise connecting connection members 862 and 867together, as will be described below. Other embodiments leave one ormore gaps in surface 874 when the anodes and cathodes are stacked.

After being stacked as discussed above, at least portions of connectionmembers 862 and 867 are connected to each other. In one embodiment,distal sections 864 and 867 are edge-welded all along surface 874. Inone embodiment, distal sections 864 and 867 are soldered along surface874. In some embodiments, portions of distal sections 864 and 867 arestaked, swaged, laser-welded, or connected by an electrically conductiveadhesive. In one embodiment, they are spot-welded.

After being connected, portions of connection members 867 and 864 areremoved or separated so that proximal sections 863 and 868 areelectrically isolated from each other.

FIG. 36A shows a portion of stack 871 after portions of distal sections864 and 869 have been removed from the stack, forming a separation 872between anode connection members 867 and cathode connection members 862.Separation 872 in the present embodiment electrically isolates section862 from section 867. Proximal sections 863 of each cathode in the stackare still coupled to each other as are proximal sections 868 of eachanode in the stack. In various embodiments, separation 872 is formed bylaser cutting, punching, and/or tool or machine cutting. In someembodiments, an electrically insulative material is inserted inseparation 872.

The battery interconnection example of FIGS. 32-36A can help preventerrors during the manufacturing steps which may cause defects in thebattery or decrease the reliability of the battery after it isconstructed. It can also help decrease the space of the interconnectionswithin the battery, which can be important if the battery is used in anapplication such as an implantable medical device. This simpleinterconnection technique allows interconnections to be made with as fewsteps as possible.

FIGS. 36B, 36C, and 36D show a cathode 843B according to one embodiment.In this example, cathode 843B includes a connection tab 844B extendingfrom the main body of the cathode. FIG. 36C shows a side view of cathode843B. FIG. 36D shows a detail of connection tab 844B. Connection tab844B includes one or more additional layers of a conductive material845B on each side of a base layer 848B. Material 845B is thick enough tomake connection tab 844B approximately as thick as the cathode itselfincluding base layer 848B and a cathode material 847B. Thus, a stack ofcathodes such as cathode 843B results in the cathode tabs of adjacentcathodes being generally flush with each other. A neck area 846B isprovided to allow room for the heat sealed separator, as discussedabove. Moreover, neck area 846B also allows for flexibility in the jointto take up manufacturing tolerance variations.

FIG. 36E shows a portion of a battery 849B having a battery stack 850Bconstructed using cathodes 843B and similarly configured anodes 851Bhaving thicker connection tabs 860B, which can be constructed by usingadditional material on one or both sides of the anode base layer. In oneembodiment, cathodes 843B are constructed of a paste cathode material asdescribed above. In some respects, stack 850B is similar to stack 814discussed above and the above discussion is incorporated herein byreference. Stack 850B allows for the cathode connection members 843B tobe connected by edge welding, a spot weld, staking, laser welding, etc.Likewise, the anode connection members 851B are connected together.Again, the thicker tab structure of the connections members 843B and851B allows for the interconnections to be made without having tosqueeze the tabs together, which may damage the structure.

FIGS. 37-40 show a battery stack 884 constructed according to oneembodiment. Battery stack 884 includes some features as discussed abovefor battery stack 24 shown and discussed in FIGS. 2-14, and the abovediscussion is incorporated herein by reference.

FIG. 37 shows a base cathode layer 880 having a terminal tab 881 and oneor more legs or extensions A, B, and C. FIG. 38 shows a base cathodelayer 882 having a terminal tab 883. And one or more legs or extensionsD, E, and F.

FIG. 39 shows battery stack 884 having a sequential stack of alternatingcathode layers and anode layers separated by a separator. Stack 884includes base cathode layer 880 and a plurality of cathode layers whichinclude a tab located in either the A, B, or C position. Likewise, stack884 includes base anode layer 882 and a plurality of anode layers whicheach include a tab located in either the D, E, or F position.

FIG. 40 shows stack 884 after the respective tabs have been connectedtogether and wrapped around the stack. As noted above, by spreading thecathode and anode interconnections out over separate areas, the overallthickness required by the interconnections is lessened and less space isneeded between stack 884 and the battery case. Terminal tabs 883 and 884are then attachable to a feedthrough or the case, as discussed above.

After being stacked, any of the battery stacks described above can betaped around the outer surface of the stack to hold the stack in strictalignment. For example, stack 814 includes a tape 828.

FIG. 41 shows a taping fixture 890 according to one embodiment. Tapingfixture 890 includes a tape dispenser 891 that holds a roll of tape 892.Taping fixture 890 includes a stack holding fixture 893 which includes astack holding member 894. A rotating member 895 is operatively coupledto stack holding member 894 and rotates the stack around a first axis896. In one example, the first axis is along the long axis of thebattery stack. Rotating member 895 can include a manual ormotor-operated crank. An indexing member 898 can be used to index andmeasure the amount of rotation of the rotating member 895.

Either one or both of dispenser 891 and fixture 893 are rotatable arounda second, vertical axis 899 so that the two members 891 and 893 arerotatable relative to each other around the second axis 899. Second axis899 is approximately perpendicular to first axis 896, and generallyvertical relative to the work surface. In one example, second axis 899approximately intersects first axis 896.

FIG. 42 shows a top view of fixture 890. As tape 892 comes off of tapedispenser 891, the tape forms an angle relative to stack 897. Byrotating the stack or dispenser about second axis 899, the angle of thetape relative to the stack can be varied.

FIGS. 43A and 43B show one example of a taping process. In use, tape 892is applied to a first surface 897A of stack 897. The stack is thenrotated along axis 896. When the tape strip 892 comes to the edge of thestack 897, the tape dispensing location swings on an arc about axis 899to match the angle of the first strip relative to the tangent line ofthe edge profile and the stack continues to rotate around axis 896.

For example, strip 892 starts out as section 1 across surface 897A ofstack 897. In this example, section 1 has an approximately 10 degreeangle relative to a perpendicular line of the edge of the stack, whichin this example is the tangent line of the edge. When the tape stripreaches the edge of the stack, the dispenser is rotated relative to thestack such that the strip is positioned along side 897B oriented assection 2 (FIG. 43B) which is approximately 10 degrees on the other sideof the perpendicular from strip 1. Thus there is a 20 degree anglebetween the two strips with approximately 10 degrees on each side of aperpendicular line to the tangent line. When the stack is then rotatedenough along axis 896 such that the tape reaches the edge of the stack,the dispenser is rotated relative to the stack such that the strip thenis oriented along section 3 (FIG. 43A). This process can be continuedthrough 2, 3, 4, or more rotations.

As can be seen by the dotted lines showing strip 2 in FIG. 43A, thetape's orientation is changed as it rounds each edge so that each sideis the matching angle of the other side relative to the perpendicular ofthe tangent line of the edge. For example, a tangent line 893 is shownat the edge between strips 2 and 3. The angles of strips 2 and 3 areapproximately equal relative to this tangent line. This technique helpseliminate bunching of the tape at the edges. Moreover, this simple andelegant solution provides for case of taping and manufacturing batterystack having non-standard, non-rectangular shapes.

FIGS. 44A and 44B show another example wrapping in accordance with oneembodiment. In this example, the tape strip is started at approximately10 degrees off the perpendicular. Strip 2 is applied approximately 10degrees on the other side of the perpendicular. (FIG. 44B). Strips 3 and4 are likewise oriented as described above.

In general, the degree of rotation of the dispenser relative to thestack is dependent on the shape of the stack. This system is general inthat it can wrap almost any shape stack. Again, this is helpful for useon complex, or oddly shaped stacks. Moreover, fixture 890 allows a stack897 to be taped in a fixture having only two rotational axes. Thissimple fixture allows taping of a stack having an arbitrarily complexgeometry in a single piece, multi-pass, taping operation.

Due to the complex geometry on the outer profile of the stack, a simpletape operation can be difficult. This system simplifies the equipmentneeded to dispense and apply a single continuous piece of tape aroundthe stack and to make multiple wraps without requiring many axes ofmotion.

Referring again to the general configuration of battery 800 shown inFIGS. 25 and 26, FIG. 45 shows further details of battery 800 accordingto one embodiment. Stack 814 is shown inserted in case 802 with aportion of case half 804 shown in broken form. The anode layersubassemblies of stack 814 have their tabs or extension members 817brought together and interconnected. A tab 822 is then attached to theanodes by welding, for example, and attached directly to case 802, bywelding, for example. The extension members or tabs 819 of the cathodesub-assemblies are brought together and interconnected and a connectionmember 824 is connected to the cathode tabs. Feedthrough post 808 isconnected to tab 824 and extends through a feedthrough hole 809 in thebattery case. The top stack portion 820 is indented relative to middlestack portion 818 to allow for maximum stack size with the curved edgecase 802.

FIG. 46 shows a top view of a portion of battery 800. Feedthrough post808 communicates outside the battery by being connected to the cathodesvia connection 824. FIG. 47A shows a cross-section of FIG. 46. In oneembodiment, feedthrough hole 809 is a cylindrical structure integralwith case 804. Hole 809 includes an inwardly facing surface defining aferrule portion 809A. Feedthrough post 808 is electrically insulatedfrom case 804 by annular insulating member 813. In one embodiment,annular insulating member 813 can be a glass member, a ceramic member,an epoxy member, or a composite member, for example. In one embodiment,annular member 813 includes TA23 glass, or equivalent. Feedthrough post808 extends through a hole in annular member 813. Feedthrough post 808can include a molybdenum material. Annular member 813 electricallyinsulates feedthrough 808 from case 802 and provides a hermetic seal ofbattery 800.

Annular insulating member 813 has an outer surface abutting the inwardfacing cylindrical surface of ferrule portion 809A. Annular member 813includes an inner hole that feedthrough post 808 extends through. In oneembodiment, annular member 813 is glassed into the battery case. Theintegral ferrule structure of this embodiment provides ease ofmanufacturing a battery since the ferrule does not need to be weldedonto the case. Moreover, it can be a cost-effective and sizeadvantageous approach for a hermetically sealed battery. By installingthe feedthrough directly into the case, a difficult welding step iseliminated since the case and the feedthrough ferrule are a combinedassembly rather that two separate subassemblies that need to be joinedtogether.

FIG. 47B shows a cross-section of FIG. 46. Anode terminal 810 isdirectly attached to case 802 to complete the connection from the anodesthrough tab 822 and via case 802 to terminal 810.

FIG. 48A shows a terminal 810B according to one embodiment. Terminal810B includes a base 64 having a surface 66. A main terminal extension63 extends from one surface of base 64 and a nipple or protrusion 65extends from opposing surface 66. Terminal 810B can be formed of a metalsuch as gold-plated nickel.

FIG. 48B shows a side view of terminal 810B being attached to a case 802in accordance with one embodiment. Case 802 is a metal, such as 304L or3161 SST. A fixture 68 is used to hold terminal 810B. Fixture 68 andcase 802 are oppositely charged. For example, fixture 68 can negativelycharged, while case 802 is positively charged by an electrode 67, orvice versa. Terminal 810B is positioned such that protrusion 65 isfacing case 802 and is the closest portion of terminal 810B to the case.As the terminal is brought closer to the case, protrusion 65concentrates or focuses the electrical field developed between theoppositely charged case and terminal. When the terminal is close enough,a spark or arc is sent between the protrusion and the case. This sparkvaporizes the nipple and welds the terminal to the case. One exampleuses a HCD125 MicroJoin™ welding machine set at 30-40 watt-sec powerlevel at 5 lb. force with a pulse width at the #4 setting on themachine.

FIG. 48C shows a view of terminal 810B after being attached to case 802.The protrusion has vaporized and surface 66 of base 64 is tightlyattached to case 802.

In some embodiments, resistance welding can also be used to attachterminal 810B to the case. For example, terminal 810B and the case canbe brought in contact and a current is delivered. Protrusion 65 thenmelts down and collapses and surface 66 and case 802 are tightlyattached.

FIG. 48D shows further details of terminal 810B according to oneembodiment. In one embodiment, base 64 includes a chamfered rear surface64S, for example of approximately 45 degrees. Front surface 66 can havean angle of approximately 3 degrees. In this example, base 64 has adiameter of approximately 0.022 to 0.030 inches and protrusion 65 has adiameter of approximately 0.005 to 0.008 inches.

After the stack is mounted within the battery case, the case can bewelded shut. An electrolyte is filled into the case through a backfillport, for example. The backfill port is then sealed.

FIGS. 49A-49B shows a technique for mounting a backfill ball plug 41 toa backfill port 901, in accordance with one embodiment. Backfill plug 41is shown being mounted to a battery case 803. Backfill port 901 in thebattery case has been used to fill the battery case with electrolyte.One problem during the mounting of backfill plugs is that theelectrolyte can leach out around the plug before the plug is welded tothe case. When this fluid leaches out, it makes welding difficult. Thepresent technique minimizes leaching and allows for a hermeticallysealed battery.

In one embodiment, a first welding electrode 902 is adapted to be usedas an applicator to force ball 41 into port 901. For example, electrode902 can be given a rounded tip to match the shape of the backfill plug.In one embodiment, plug 41 can be a spherical-shaped ball having adiameter slightly larger than port 901 such that there is aninterference fit between plug 41 and the walls 901A defining port 901.For example, in one embodiment, plug 41 has a diameter of approximately0.026 inches and port 901 has a diameter of approximately 0.025 inches.As applicator/electrode 902 forces plug 41 into port 901, a secondwelding electrode 903 is applied against case 803. A current developsbetween electrode 902 and 903 traveling through plug 41 and case 803.This welds the periphery of plug 41 to the case at weld location 905.This welding technique seals the ball within the port without allowingany leaching of electrolyte through the gap between the ball and theport walls.

In one embodiment, after weld 905 is formed, electrodes 903 and 902 areremoved and the battery is sealed. In other embodiments, as shown inFIG. 49C an optional laser welding step is provided by a laser welder907 to further seal the upper periphery of the ball-shaped plug 41 tothe case.

FIGS. 50A shows a backfill plug 910 according to one embodiment. Plug910 is a cap-shaped plug having a top portion 911. In one embodiment,top portion 911 expands outward to cap portion 912 defining a chamferedregion 916 between top portion 911 and cap portion 912. Plug 910includes a waist section 913 which expands into a widened section 914and then a narrowed section 915. In one embodiment widened section 914is slightly wider than the diameter of backfill port 901. For example,widened section 914 can be approximately 0.026 inches and backfill port901 can be approximately 0.025 inches in diameter.

FIGS. 50B and 50C shows an example of plug 910 being mounted to backfillport 901. An applicator electrode 917 is adapted to insert and forceplug 910 into backfill port 901 in an interference fit. During or afterapplicator/electrode 917 forces plug 910 into port 901, a second weldingelectrode 903 is applied against case 803. A current develops betweenelectrodes 910 and 903 traveling through plug 910 and case 803. Thiswelds the widened portion 914 of plug 910 to a wall 901A of the case atweld location 919. Again, this technique of welding while forcing sealsthe plug within the port without allowing any leaching of electrolytethrough the gap between the plug and the port walls.

In one embodiment, as shown in FIG. 50C an optional laser welding stepis provided by a laser welder 907 to laser weld the periphery of the cap912 of plug 910 to the outer surface of case 803. By providing achamfered region 916, the laser welding step is improved. FIG. 50C showshow plug 910 fits within port 901. Cap portion 912 rests against theouter surface of case 803. Waist portion 913 is located inside of andnot touching the walls of port 901. In one embodiment, plug 910 isformed from stainless steel.

FIG. 50D shows a terminal 810C according to one embodiment. Terminal810C is a combination backfill plug/terminal. Terminal 810C includes anelongated terminal portion 63C and a spherical plug portion 41C. Plugportion 41C is dimensioned to interference fit within backfill hole 901.In one embodiment, terminal 810C can be attached within the backfillhole 901 and be coupled to the case 803 using the techniques discussedabove. For example, a welding fixture 902 can be used to bring terminal810C within the backfill hole 901 and in contact with case 803 as asecond welding electrode 903 is brought against the case to weld thespherical ball portion 41C within the hole, as in FIGS. 49A-49C. Thecombination terminal 810C allows for the elimination of separateterminals and fill plugs (such as terminal 810 and plug 41 discussedabove). By combining the two members, manufacturing is eased.

FIG. 50E shows a terminal 810D according to one embodiment. Terminal810D is a combination backfill plug/terminal. Terminal 810D includes anelongated terminal portion 63D and a plug portion 910D. Plug portion910D is similar to plug 910 discussed above and the above discussion isincorporated herein by reference. As with terminal 810C, terminal 810Dcan be attached within the backfill hole of a battery case.

In various embodiments of the techniques and structures of FIGS. 49A-49Cand 50A-50E, a parallel gap welder can be used to perform the weld.Various embodiments utilize a current of approximately 10 toapproximately 45 watt-sec or higher. One embodiment uses a HCD125MicroJoin™ welder with settings of 30 watt-seconds and 2 lb. force andpulse width at the #4 setting.

FIG. 51 shows a method for manufacturing a battery in accordance withone embodiment. The method of FIG. 51 is an example of one embodimentand it is understood that different steps may be omitted, combined,and/or the order changed within the scope of one or more embodiments.Among other steps, method 51 includes assembling an anode subassembly(930A), assembling a cathode subassembly (930B), stacking a plurality ofanode and cathode subassemblies into a battery stack (930C), welding thetabs of each of the anode subassemblies together and welding each of thetabs of each of the cathode subassemblies together and taping the stack(930D), providing a battery case for holding the stack (930E),insulating the outer surface of the stack and inserting the stack intothe case (930F), welding the anodes to the case (930G), welding thecathodes to a feedthrough (930H), assembling the feedthrough assemblyincluding glassing the feedthrough through a feedthrough insulator(930I), welding the case shut and filling the case with electrolyte(930J), and inserting and welding a backfill plug to the case (930K).

In one embodiment, assembling the anode sub-assembly (930A) can includeforming a plurality of discrete anode layers such as the various anodesdiscussed above. FIG. 52 shows a schematic representation of an anodeassembly system 940 according to one embodiment. System 940 includes afirst spool 941 holding a roll of metal base anode material, such as anexpanded metal, a solid metal, or an etched metal. A pair of spools 942Aand 942B provide a layer of lithium on either side or both of the basematerial. One or more brushes 946A and 946B clean the lithium layers.The lithium is laminated onto the base layer at a stage 943. A die-cutmechanism 944 cuts the individual anodes, and a robotic system 945removes them.

FIG. 53 shows a schematic system 950 for forming cathode layersaccording to one embodiment. A first spool 951 holds a base cathodematerial. A die cut system 952 cuts the layer to a desired shape. A heatseal system 954 can be provided to seal the separators around thecathode. The cathode assembly can then transferred by a robotic system953.

FIG. 54 shows a schematic representation of a fixture 1960 for forming acathode in accordance with one embodiment. Fixture 1960 provides atechnique to load a predetermined, precise amount of a cathode powderonto a cathode carrier strip for use in the manufacture of cathodelayers of a battery. Fixture 1960 generally includes a pair of dies orclamp members 1961A and 1961B. One or more guide posts 1964 extend fromthe inner surface of one of the clamp members 1961A and 1961B. Theopposing clamp member includes corresponding holes which mate with theguide posts to keep the pair of members 1961A and 1961B in alignmentwhen they are brought together. Each of the clamp members 1961A and1961B include a cut out or cavity portion 1969.

A cathode carrier strip 1966 includes a cathode base section 1967 andone or more guide holes 1968. Guide holes 1968 mate with guide posts1964 to keep the cathode carrier strip 1966 tightly aligned in fixture1960.

Fixture 1960 includes a pair of punch members or press heads 1962A and1962B. Each punch member 1962A and 1962B is associated with one of clampmembers 1961A or 1961B such that each punch member moves back and forththrough cut-out portion 1969.

In use, a preset amount of MnO₂ matrix material is poured into thecavity in the bottom clamp member 1961B. In one example, the MnO₂ powderincludes a mixture of 90% pure MnO₂, 5% powder carbon, and 5% PTFEslurry binder. A flat edge tool is used to spread the MnO₂ powder evenlyin the cavity. The collector strip 1966 is placed in position over thecavity. A shim 1980 is placed onto the collector strip and fastened downto hold in position. A preset amount of MnO₂ matrix material is pouredinto the cavity 1981 of the shim. The flat edge tool is used to spreadthe powder evenly in the shim cavity. Top clamp member 1961A is thenpositioned over and fastened to the bottom clamp member.

FIG. 55 shows a press 1963 applying force to punch members 1962A and1962B. The fixture 1960 is placed into press 1963 and the press iscycled with several pressures in steps from low pressure to highpressure until the powder is compacted to the desired density. In oneembodiment, a pressure of approximately 48,000 psi is used. In oneembodiment, a pressure of approximately 16-21 tons per square inch isused.

In one embodiment, fixture 1960 is mounted to a vibrating system whichis actuated to vibrate the fixture either after the powder is placedwithin the cavities. The vibration settles the powder to fill any gapsand makes the powder have a generally uniform density within thefixture.

Since the size of the cavities of the fixture and the density of thecathode powder is known, a precise amount of powder is compacted ontothe carrier strip. Battery cathodes that are later punched or removedfrom the strip then contain precise amounts of the cathode powder andthe cathode powder is evenly distributed across the surfaces of thecathode carrier in a uniform density. This improves the consistency andreliability of the batteries. In one example, the powder has a presseddensity of approximately 2.7 g/cm³ and the cathode has an overallthickness (including base metal) of approximately 0.0182 inches. Otherembodiments an range form approximately 2.5 to 3.2 g/cm³.

FIG. 56 shows a schematic representation of a fixture 960 for forming acathode in accordance with one embodiment. Fixture 960 provides atechnique to load a predetermined, precise amount of a cathode powderonto a cathode carrier strip for use in the manufacture of cathodelayers of a battery. Fixture 960 generally includes a pair of clampmembers 961A and 961B. One or more guide posts 964 extend from the innersurface of one of the clamp members 961A and 961B. The opposing clampmember includes corresponding holes which mate with the guide posts tokeep the pair of members 961A and 961B in alignment when they arebrought together. Each of the clamp members 961A and 961B include a cutout portion 969. When clamp members 961A and 961B are brought together,cut out portions 969 define a cavity 970.

A cathode carrier strip 966 includes a cathode base section 967 and oneor more guide holes 968. Guide holes 968 mate with guide posts 964 tokeep the cathode carrier strip 966 tightly aligned in fixture 960 suchthat cathode base section 967 is located within cavity 970.

Fixture 960 includes a pair of punch members or press heads 962A and962B. Each punch member 962A and 962B is associated with one of clampmembers 961A or 961B such that each punch member moves back and forththrough cut-out portion 969. A press 963 applies force to punch members962A and 962B. A punch surface 971A and 971B of each respective member962A and 962B is brought close together within cavity 970.

FIG. 57 shows an example of carrier strip 966 mounted in a substantiallyvertical orientation within fixture 960. Members 961A and 961B areclamped together to hold the carrier strip 966 in place. A cathodepowder 972, such as an MnO₂ mixture, is placed or deposited withincavity 970. In one embodiment cavity 970 has a width of approximately0.030 to 0.040 inches. In one example, powder 972 includes a mixture of90% pure MnO₂, 5% powder carbon, and 5% PTFE slurry binder.

In one embodiment, fixture 960 is mounted to a vibrating system 974which is actuated to vibrate the fixture either during or after thepowder is placed within cavity 970. The vibration settles the powder tofill any gaps and makes the powder have a generally uniform densitywithin cavity 970. In one embodiment, a precise amount of powder 972 isplaced within cavity 970. The amount of cathode powder can be varieddepending on application of the cathode.

After cavity 970 is activated, press 963 is activated and punch members962A and 962B press the powder into and onto the base carrier 966. Inone embodiment, a 50 ton press 963 is utilized. In one embodiment, apressure of approximately 48,000 psi is used to press the powder.Another example uses a pressure of approximately 16-21 tons per squareinch.

In one embodiment, cathode powder 972 is sieved before it is depositedinto the cavity to prevent any larger pieces of the powder to clog upthe cavity.

Since the size of cavity 970 and the tap density of the cathode powderis known, a precise amount of powder is compacted onto the carrierstrip. Battery cathodes that are later punched or removed from the stripthen contain precise amounts of the cathode powder and the cathodepowder is evenly distributed across the surfaces of the cathode carrierin a uniform density. This improves the consistency and reliability ofthe batteries. In one example, the powder has a pressed density ofapproximately 2.7 g/cm3 and the cathode has an overall thickness(including base metal) of approximately 0.0182 inches. Other embodimentsan range from approximately 2.5 to 3.2 g/cm³.

FIGS. 58, 59, and 60 show a top, side and front view of a cathodeforming fixture 974 according to one embodiment. Fixture 974 includesbase tabs 975 to mount the fixture to a surface. Clamps 976A and 976Bhold a carrier strip within the fixture with a guide member 984 to holdthe carrier strip and to keep the two halves of fixture 974 inalignment.

A pair of punch heads 977A and 977B each have a punch member 983A and983B associated therewith. The area between the punch members 983A and983B defines the cavity of the fixture. A spring 980 is positionedbetween each punch head 977A and 977B and its associated punch member983A and 983B. A pair of plug members 978A and 978B are located on topof the fixture, and each plug member has a thumbscrew or other retainingmember 979 engaged through the plug and into a block member 981 or 982located below the plug. A guide post 982 provides further alignmentbetween the two halves of the fixture. A bushing 982 can be used aroundguide post 982.

As noted above, some embodiments use a cathode paste (such as an MnO₂paste) which is coated and then rolled or pressed onto one or more sidesof a cathode base layer, such as stainless steel strip or a mesh strip.Individual cathodes can be then excised out of the strip. In someexamples, the base layer is at least partially pre-cut or pre-scoredinto the desired cathode shape.

Referring again to FIG. 51, forming a cathode sub-assembly (930B) caninclude encapsulating each cathode in a separator envelop, as discussedabove.

In one embodiment, the present system provides a battery electrode stackhaving 12 anode sub-assemblies and 11 cathode sub-assemblies (havingsealed separators). The two anode sub-assemblies located on the stackends are smaller to accommodate a radius case edge. These two end anodesub-assemblies have lithium attached to one side of their base collectorplate only. The two outside cathode sub-assembly layers are also smallerin order to accommodate the radius of the case. Each anode and cathodesub-assembly layer includes an extension tab that extends out of thestack. The extension tabs are welded together when the stack iscompleted in order to connect the layers to one another. In one example,the extension tabs are welded with three spot welds and the ends of thetabs are clipped. A ribbon tab is welded to the cathode extensions forconnecting them to the feedthrough. The cell is insulated and insertedinto the case. The ribbon extension is welded to the feedthrough and theanode extension is welded directly to the case. The case portions areput together and welded around their interface.

FIG. 61 illustrates one of the many applications for the battery. Forexample, one application includes an implantable medical device 990which provides therapeutic stimulus to a heart muscle, for instance, adefibrillator or a cardiac resynchronization therapy device (CRTD). Themedical device 990 is coupled with a lead system 991. The lead system991 is implantable in a patient and electrically contacts strategicportions of a patient's heart. The medical device 990 includes circuitry992 which can include monitoring circuitry, therapy circuitry, and acapacitor coupled to a battery 993. Circuitry 992 is designed to monitorheart activity through one or more of the leads of the lead system 991.The therapy circuitry can deliver a pulse of energy through one or moreof the leads of lead system 991 to the heart, where the medical device990 operates according to well known and understood principles. Theenergy of the device are developed by charging up the capacitor by usingbattery 993.

In addition to implantable defibrillators, the battery can beincorporated into other cardiac rhythm management systems, such as heartpacers, combination pacer-defibrillators, congestive heart failuredevices, and drug-delivery devices for diagnosing or treating cardiacarrhythmias. Moreover, the battery can be incorporated also intonon-medical applications. One or more teachings of the presentdiscussion can be incorporated into cylindrical batteries.

FIG. 62 shows a performance chart of an example battery constructedaccording to one embodiment. The battery of FIG. 62 was constructedhaving anodes and cathodes having the values shown in Chart A, below,and was formed in the manner of battery stack of FIG. 27.

Active Estimated Total Area Volume Material Capacity Type Quantity Area(cm2) (cm2) (cc) Mass (g) (A-h) Anode-small  2 surfaces 7.526 15.050.1147 0.0612 0.236 (2 anode layers) Anode- 20 surfaces 8.013 160.261.2211 0.652 2.517 large (10 anode layers) Total 15.539 175.31 1.33580.7132 2.753 Cathode-  4 surfaces 7.796 31.184 0.6812 1.6552 0.3724small (2 cathode layers) Cathode- 18 surfaces 8.29 149.22 3.2596 7.92071.7821 large (9 cathode layers) Total 16.086 180.404 3.9407 9.576 2.1546Ratio 1.278 Li/Mn02 Cathode 0.017 a/cm² current density

A total of 12 lithium anodes were used, with the anodes on each end ofthe stack only having one surface with lithium and having a smaller areathan the other anodes. The chart indicates that the two end anodes eachprovide one anode surface with the remainder of the anodes providing twoanode surfaces each. A total of 11 MnO₂ cathodes were used, with the endtwo cathodes being of smaller surface area. All the cathodes had bothsurfaces having MnO₂, so the chart indicates four small cathode surfacesand 18 large cathode surfaces. The cathodes were prepared using aprecisely measured amount of cathode powder pressed into the base layer,as discussed above.

After being pressed, the cathodes were heat-sealed between twoseparators, as discusses above. The anodes and cathodes were thenalternatingly stacked using the fixture of FIG. 18B. The stack was thentaped using the fixture of FIG. 41. The outer periphery of the stack wasthen taped by a double wrapping of an insulative tape as in FIG. 26B.The anode and cathode extension tabs were brought together and welded.The cathode tabs were connected to the feedthrough and the anode tabswere connected to the case. The case portions were put together andwelded around their interface. The battery was filled with electrolyteand sealed using techniques discussed above.

The battery of chart A and FIG. 62 was designed for an implantablemedical device, such as a defibrillator. The battery was designed tohave a capacity of approximately 2.0 amp-hours with a life span of 6 to7 years and a peak current level of approximately 3 amps. Using themethods and structures discussed herein, the battery was constructed tosuch specifications while having a shape friendly design suitable forfitting into a design space within the defibrillator case and while onlyhaving a total volume of 8.64 cm³.

In various embodiments, batteries for different applications can beconstructed using various design parameters. For example, someembodiments have a total battery volume of less than approximately 9.0cm³. Some embodiments have a total battery volume of betweenapproximately 8.0 cm³ and 9.0 cm³. Some embodiments have a total batteryvolume of between approximately 8.5 cm³ and 9.0 cm³. Some batteries havea power of approximately 2 to 5 amps and a capacity of approximately 2.0amp-hours or greater. Other batteries can be manufactured using thetechniques herein for different applications. Various embodimentsinclude batteries having sizes ranging from about 3.0 cm³ to about 12cm³. In general, the capacity in amp-hours/cm³ of these different sizebatteries scales up linearly

Referring again to FIG. 62, the charge time A of the battery is seen tobe substantially constant over the useful life of the battery. Forexample, with a 2-4 amp current drain, in one embodiment, the chargetime is generally about 6 to 7 seconds. Some embodiments have asubstantially constant charge time between approximately 5 to 10seconds. The line C in FIG. 62 denotes the open circuit voltage (OCV) ofthe battery. The line B denotes the Pulse One Average (P1A) of thebattery. In one example, the P1A can be used to trigger ERI (electivereplacement indicator). This triggers a 3 month clock until EOL (end oflife). In the present example, EOL is approximately when OCV reaches2.75 volts or when P1A reaches 1.75 volts.

The battery of FIG. 62 can also be constructed using a paste cathodeconstruction, as discussed above. Moreover, the other anode and cathodeinterconnection techniques discussed above can also be used to constructa battery of the desired characteristics.

In one or more embodiments, the above described methods and structuresprovide for a battery making efficient use of space within the case,increased electrode surface area and increased capacity for a battery ofa given set of dimensions. In one example, variation in the outerdimensions of one battery stack to another battery stack is reducedbecause each is formed of a precisely aligned series of electrodelayers. Dimensional variations in the battery stack resulting fromvariation in the reference points from case to case or alignmentapparatus to alignment apparatus can be reduced or eliminated. Thisprovides improved dimensional consistency in production and allows forreduced tolerances between the battery stack and the battery case. Thisallows for more efficient use of space internal to the battery case.

In one or more embodiments, different battery chemistries can be usedfor the cathode structures discussed above. For example, silver vanadiumoxide (SVO), carbon monoflouride (Cfx), and carbon vanadium (CVO) can beutilized in accordance with some embodiments. In addition to primarybatteries, batteries according to some embodiments can be formed assecondary type batteries or rechargeable batteries such as Lithium ion.

It is to be understood that the above description is intended to beillustrative, and not restrictive. Many other embodiments will beapparent to those of skill in the art upon reading and understanding theabove description. It should be noted that embodiments discussed indifferent portions of the description or referred to in differentdrawings can be combined to form additional embodiments of the presentinvention. The scope of the invention should, therefore, be determinedwith reference to the appended claims, along with the full scope ofequivalents to which such claims are entitled.

1. A battery stack comprising: a plurality of alternating anode andcathode layers, each of the cathode layers having a base layer and acathode material layer attached to the base layer, the base layerincluding a cathode tab extending from a first position, each cathodetab having a thickness greater than a thickness of the cathode baselayer; and wherein each anode layer includes an anode tab extending froma second position.
 2. The battery stack of claim 1, wherein each anodelayer includes a base material layer and wherein each anode tab has athickness greater than a thickness of the anode base material layer. 3.The battery stack of claim 1, wherein each of the anode and cathodelayers includes a substantially non-rectangular shape.
 4. The batterystack of claim 1, wherein the cathode material layer includes MnO₂. 5.The battery stack of claim 4, wherein the MnO₂ layer does not cover thecathode tab.
 6. The battery stack of claim 1, wherein the base layerincludes a metal sheet.
 7. The battery stack of claim 1, furtherincluding a separator layer between each anode layer and each cathodelayers.
 8. The battery stack of claim 7, wherein an outer perimeter edgesurface of each cathode layer is offset from an outer perimeter edgesurface of each anode layer that is adjacent to the cathode layer. 9.The battery stack of claim 8, wherein the outer perimeter of eachcathode layer is completely offset from the outer perimeter of eachanode layer.
 10. The battery stack of claim 7, wherein each separator isconnected to an adjacent separator to form a substantially sealed pocketaround each cathode layer.
 11. The battery stack of claim 10, whereinthe tab of each cathode layer is exposed beyond the substantially sealedpocket.
 12. The battery stack of claim 1, wherein each cathode layer hasa first separator on one side and a second separator on a second side,wherein the first separator and the second separator are connected toeach other around at least a portion of their edges.
 13. The batterystack of claim 12, wherein the first separator and the second separatordefine a flange at the connection of the first separator and the secondseparator, wherein the flange extends beyond an edge of the cathodelayer and encloses the edge of the cathode layer.
 14. The battery stackof claim 13, wherein the connection between the first separator and thesecond separator includes a heat seal.
 15. The battery stack of claim 1,wherein each of the plurality of cathode layers is stacked such that thecathode tabs of each cathode layer overlay one another and wherein eachof the plurality of anode layers is stacked such that the anode tabs ofeach anode layer overlay one another.
 16. The battery stack of claim 1,wherein the cathode tabs are approximately as thick as a combinedthickness of the cathode base layer and the cathode material layer.